The present invention relates to a continuous process for hydrogenating nitriles by means of hydrogen in the presence of a catalyst in a reactor, where the catalyst is arranged in a fixed bed, wherein the cross-sectional loading in the reactor is in the range from 5 kg/(m2 s) to 50 kg/(m2 s).
The present invention further relates to a process for preparing downstream products of isophoronediamine (IPDA) or N,N-dimethylaminopropylamine (DMAPA) from amines prepared according to the invention.
In the hydrogenation of nitriles to form the corresponding amines, it is frequently necessary to achieve a high conversion of the nitriles used, since unreacted or only partially reacted nitriles are difficult to separate off, can undergo secondary reactions and can lead to undesirable properties such as odor and discoloration in subsequent applications. Furthermore, it is frequently desirable to achieve a high selectivity in respect of the formation of primary amines from primary nitriles and to avoid the formation of secondary and tertiary amines.
The hydrogenation of nitriles is generally carried out by catalytic hydrogenation over noble metals such as Pt, Pd or rhodium or Co and Ni catalysts (see, for example, “Amines, Aliphatic”, Ullmann's Encyclopedia of Industrial Chemistry, Published Online: 15 Jun. 2000, DOI: 10.1002/14356007.a02—001).
The process is usually carried out in the suspension mode or in a fixed-bed reactor.
In the suspension mode, the catalyst used has to be separated off from the reaction mixture in order to make an economical process possible. The separation is associated with a process engineering outlay.
When catalysts based on Co, Ni or Cu are used, very high temperatures and pressures are generally necessary in the hydrogenation in a fixed bed in order to reduce the formation of secondary and tertiary amines which can be formed by reaction of primary amine with partially hydrogenated nitrile (=imine intermediate).
For example, EP-449089 discloses the hydrogenation of isophoronenitrile to isophoronediamine at 250 bar and WO 2007/128803 describes the hydrogenation of N,N-dimethylaminopropionitrile (DMAPN) to N,N-dimethylaminopropylamine (DMAPA) at 180 bar.
These drastic reaction conditions can increase the formation of other undesirable by-products and require a high outlay for materials and to ensure safety.